01 - Heat olive oil in a large pot over medium heat. Add onion, carrots, celery, and red bell pepper. Sauté for 6–8 minutes until softened.
02 - Add garlic and cook for 1 minute until fragrant.
03 - Add ground beef. Cook, breaking it up with a spoon, until browned and no longer pink.
04 - Stir in tomato paste, oregano, basil, bay leaf, and red pepper flakes. Cook for 2 minutes.
05 - Add lentils, diced tomatoes with juice, and broth. Stir well, scraping up any browned bits from the bottom.
06 - Bring to a boil, then reduce heat to low. Cover and simmer for 35–40 minutes, stirring occasionally, until lentils are tender and sauce is thickened. Add more broth or water if needed.
07 - Season with salt and pepper to taste. Remove bay leaf.
08 - Serve hot over whole wheat pasta, zucchini noodles, or rice. Garnish with fresh herbs and Parmesan if desired.